Insulating composition.



UNITED STATES PATENT OFFICE.

LEOH. BAEKEIIAND,- 0F YONKERS. NEW YORK, ASSIGNOR T0 GENERAL BA KELITE COMPANY, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

INSULATING COMPOSITION.

no Drawing.

* Certain condensation products of phenols and formaldehyde have received, on account of their infusibility and insulating properties, important applications in electrical engineering. These substances, as heretofore used,-have, however, certain decided drawbacks, which considerably interfere with some of their electrical uses. For instance,

the act of hardening, or polymerization, is

accompanied by a considerable reduction in volume or shrinkage; moreover, the final product is hard and inflexible, and does not lenditself readily-to bending. Furthermore, the temporarily fusible and soluble initial condensation products, which constitute the preferred starting point for the formation of the infusible end products, and which are used in liquid form for the impregnation of coils, contain usually more or less large quantities of water, bodies, or both together, or of solvents, It is a known fact that the presence ofwater, or free phenolic bodies or other bodies con taining hydroxyl groups is detrimental for insulatingpurposes, where alternating currents of high voltage are used. If we try to eliminate the above impurities by evaporation, the mass becomes so 'thick as to render it unsuitable for impregnation purposes. If in order to liquefy the mass, heat be applied, the first efi'ect of'the heat may indeed produce a more liquid condition, butt-his is rapidly followed by objectionable thickening, on accountof polymerization. This thickening can be preventedby the introduction of a certain amountv of alcohol or acetone or similar liquids, these solvents then forming with the initial products of condensation, a solution or varnlsh. But if the desired flu? idity is thus insured, the other drawbacks are not eliminated. For instance, these low-- boiling-point solvents are expelled by evap- Specification of Letters Patent.

or of free phenolic.

Patented Oct. '12, 1915.

oration, and this brings about a still further increase in the shrinkage of the final product. In other terms, the cause of shinkage will then be twofold; first, the shrinkage determined by polymerization and the resulting reduction of volume; second, the shrinkage superinduced by the evaporation of the liquid. llhe effect of shrinkage may become so decided that it develops cracks, voids and deformations, and irregular tension stresses in the interior of the mass. These factors are liable to cause serious irregularities in the impregnation of electric coils, thus treated; for instance, interior voids or air-holes. These air-holes are dangerous, not only on account of imperfect insulation, but .IIIOIG especially because in case of overload, they become points of maximum over-heating by the fact that air is a poorer conductor of heat than the impregnating material'itself: hence local burnouts may result. even if all above-mentioned defects did not exist, we are still confronted with the fact that the impregnating material is unusually hard and inflexible, and that Wires, or other conductors coated with the same, or embedded therein, cannot well be-bent or removed without cracking the insulating material. This factor is specially objectionable .when repairs have to be made on impregliquefiable solvent of high boiling-point, of high dielectric properties, immiscible with water, and used in quantities sufficiently small, so that there is no necessity of expelling it by evaporation, so that it may. re-

rated in the final mass, after the latter has solidified to a jelly, and this Without disturbing' its value as an insulator. Such'a solvent brings about entirely new conditions. It gives a mass which'is iliquid at normal or somewhat higher temperatures and can be But - main for the greater part at least incorpo- V used as an impregnating fluid, and which can be heated gently for a relatively long time without the danger of too rapid thickening by polymerization at lower temperatures. This is probaly due to the diluent action of the solvent, which reduces the speed -of polymerization. This liquid solution, submitted to a gradually higher temperature, say from 70 to 90 or 100 0., or over, sets to a gelatin-like mass, of very desirable elasticity' But although this mass, solidified by heat, is elastic while it is hot, it is completely infusible. Very long application of heat may harden it further without, however, removing entirely the property of softening by heat which imparts to it elasticity or flexibility. This softening action of heat permits easy removal of damaged parts in dynamos, motors, coils, etc. All that is necessary to accomplish this is a local application of heat to soften the m aterial to the point where it can easily be cut.

Owing to the' fact that the solvent is entirely composed of substances which are immiscible with water and have no affinity for water, 1t is far less sensitive to moisture than if water-absorbing substances, like free phenols, alcohol, glycerin, or similar materials werepresent. Furthermore, the ehmlnation of water from the initial condensation prodnets of phenols and formaldehyde in the preparation of my mixtures become a much easier problem than if the solvent itself had a tendency to retain water. On account of its high boiling-point, the solvent remains in the mass, harmless and unexpelled throughout the range of working temperatures, so that the objectionable reduction of volume, or shrinkage by evaporation, which occurs unavoidably whenever low-boilingpoint solvents, like alcohol, are used, does not interfere; furthermore, it brings about the increased elasticity, a most desirable factor,

which contributes still interior stresses.

Another very important advantage is the fact that the active condensation product is further .to prevent diluted by a notable proportion of an inert solvent, which practically does not participate inthe chemical action, so that the shrinkage by polymerization of the total mass is reduced to a very minimum, .or to such a point that it is no longer objectionable. This shrinkage-reducing effect can be still further increased by the addition of solid, inert substances, or powdered fillers,

as for instance, finely-powdered silex, china clay, baryta, certain oxids of iron, and in general suchfillers as are good electrical insulators and possess also a fair degree of heat conductivity, thereby aiding in a most important function, viz., the prove: 'on of overheating of dynamos, motors, or insulators. In this respect the composition is decidedly superior to ordinary resinous impregnating compounds.

The solvents used should have a boilingpoint not below 120 C., and preferably a considerably higher boiling-point, say about 200 0., or over. If too much solvent be used, the solution does not become infusibl or solidified by the application of'heat, without first being submitted to evaporation to expel the excess of solvent. A suitably limited proportion of solvent, on the contrary. renders possible direct impregnation, with the liquefied mass, follows by solidification, through further application of heat, without the necessity of evaporating any excess of solvent. The solvent can be added to the initial soluble condensation products after the latter have been suitably relieved from free water or other objectionable impurities;

'or the solvent can be introduced directly at any stage of the reaction which engenders the soluble condensation products, and water can be eliminated afterward, by any known methods, before final hardening. Either in the initial reaction, or during the final act of rendering infusible by heat, so-called hardening agents, or condensation agents, may be used to good advantage, and these can be added at any phase of the process, and either before or after the solution has been made. But I find that the very best results are obtained by the use of alkalies or bases, for instance ammonia or amins or small amounts of sodium hydroxid as condensing or hardening agents.

For theimpregnation of coils, I simply fill or impregnate the latter with the liquid mass according to known impregnation methods; then after impregnation has taken place, the coils are heated in a stove, raising the temperature gradually from C. to

100 (1., or above, taking care not to elevate the temperature too much until the impregnating liquid has coagulated to a gelatinlike mass, after which the temperature can be increased further until the product has acquired the desired consistence. Instead of heating in a stove, the heating can be carried out in a closed vessel, so that a counterpressure can be exerted during the heating, in which case the temperature can be increased very rapidly, and all operations can be pertages over those heretofore used, because once hardened by heat it has lost the property of liquefying under further application of heat. My insulating mass can be hardened at a temperature lower than that at which wooden containers are affected by heat, so that the liquefied compound can simply'be poured around the coil in the box and the Whole submitted to solidification by a further application of heat, becoming sufliciently solid to support the coil under all conditions of use. Ithas the advantage over rubber compounds of not liberating sulfur.

Among the solvents which can be used for my purposes, I may mention'naphthalene and anthracene or a' mixture of both; these substances are relatively inexpensive and fulfil the desired requirements. They can be'used alone, or together, but decidedly better in conjunction with other suitable solvents, for instance liquid cyclic hydrocarbons such as toluene, xylene, cumene, trimethylbenzene and their homologues, which are found mixedin the higher boiling liquid hydrocarbons extracted from coaltar, this mixture being usually termed neutral oil.

Sometimes it is found advantageous, in order to increase still further the fluidity of the impregnating mass, to add other liquid solvents immiscible with water and of'high boiling-point, as for instance nitrobenzene,

nitrotoluene, camphor-oil, terpenes, high-boiling-point ketones, etc., the words high-boiling-point referring to boiling temperatures of at least 120 0. In

this process the boiling-points of the individual constituents ofthe solvent. are of less importance than the boiling-point of the compound mixture of the solvent; so that cyclic hydrocarbons of relatively low boillug-point may be used in small proportion in conjunction with others of which the boiling-point is considerably higher, the mixture of both being thus rendered less volatile than if the low-boiling solvents were used alone. q r

If naphthalene be used alone and in large proportions, it has the disadvantage of giving to the product a crystalline texture and of escaping by. sublimation under the action of heat. I obviate this difiiculty by introducing into the mixture certain isubstances,

'for example liquid cyclic hydrocarbons, ni-

trobenzene, nitrotoluene, and the like. I have further found that whereas benzene, xylene, eumene, and similar hydrocarbons do not directly dissolve the initialcondensation product, either solid or liquid, to amaterial extent, yet the presence of naphthalene renders it possible to prepare solutions in such liquid cyclic hydrocarbons; For example the initial condensation product may be directlydissolved in a mixture of naphthalene and a liquid cyclic hydrocarbon, or it may be first dissolved in melted naphthalene and the mixture further diluted or dissolved in the liquid hydrocarbons, as desired. In this process, instead of using phenol, I can use its homologues or mixtures thereof, or their equivalents, and instead of formaldehyde, I can use its polymers, or substances which engender formaldehyde in this reaction, or substances which are the technical equivalents of formaldehyde. Hexamethylenetetlose its property of becoming infusible by sufficient application of heat. Instead of using directly an initial condensation product which is transformable by heat into an infusible product, such initial product may be formed indirectly in the mass by using a soluble, fusible condensation product in conjunction with formaldehyde, 'or an equivalent thereof, for example hexamethylenetetramin'.

Certain illustrative compositions in ac cordance with the present invention are as follows, it being understood that the invention is not limited to the specific components or proportions mentioned in these illustra- Commercial xylene or other suitable phenolsand formaldehyde '15 tive examples Ewample 1.

' Parts by 7 weight. Solid initial condensation product 100 Naphthalene 30 Commercial xylene or other suitable liquid cyclic hydrocarbon '30 E wample 2. 'I 'Parts by v Q weight. Solid initial condensation product 100 Naphthalene. 30

Commercial Xylene or other suitable liquid cyclic hydrocarbon 3O Paraform 3 Ewample 5.

Parts by weight. Novolak 100 Naphthalene Commercial Xylene or other suitable liquid cyclic hydrocarbon 30 Hexamethylenetetramin 4 In this application or in my claims I designate as initial-condensation product [any substances derived directly or indirectly from the condensationof phenols and formaldehyde, or their equivalents which are s -characterized by the fact that -they are .fu sible or soluble and can be transformed by the action of heat into infusible bodies.

claim: 1. An insulating composition for impregating coils or like purposes, containing a or mobile at normal or somewhat higher phenolic condensation product and a solvent therefor, said .solvent being immiscible with water, possessing high dielectric properties, and having a boiling point above 120 C., the components of the composition proportioned to render the mass fluid or mobile at normal or somewhat higher temperatures, but transformable at higher temperatures Em an infusible mass which is elastic while ot. Y

2. An insulating composition for impregnating coils or like purposes, containing a phenolic condensation product and a solvent therefor, said. solvent being a liquid im miscible with water,"'possessing high dielectric properties, and having a boiling-point above 120 C., the components of the composition proportioned to render the mass fluid temperatures, but transformable at higher temperatures into an infusible mass which is elastic while hot. n

3; An insulating composition for impregnating coils or like vpurposes, containing a phenolic condensation product. and a solvent therefor, said solvent being immiscible with water, possessing high dielectric pro erties, having a boiling-point above 120 said condensation product and solvent ro portioned to render the mass initially uid or mobile at normal or somewhat higher temperatures, but transformable by heat, without substantial evaporation, into an infusible, more or less gelatinous mass, softening under the effects of heat.

4. An insulating composition for impregsubstantial evaporation, into an infusible,

more or less gelatinous mass, softening under the efl'ects of heat.

5. An insulating composition for impregnating coils or like purposes, contaimng a phenolic condensation product and a solvent therefor, said solvent being a liquid immiscible with water, possessing high dielectric properties, having a boiling-point above 120 C., and containing a plurality of liquid cyclic hydrocarbons, said condensation product and solvent proportioned .to render the mass initially fluid or mobile at normal or somewhat higher temperatures, but transformable by heat, withoutsubstantial evaporation, into an infusible, more or less gelatinous mass, softening under the effects of heat. a

6. An insulatin composition for impregnating coils or phenolic condensation product and a solvent therefor, said solvent being immiscible with water, possessing high dielectric pro erties, having a boiling-point above 120 and containing a liquid cyclic hydrocarbon and a solid hydrocarbon, said condensation product and solvent proportioned to render the mass initially fluid or mobile at normal or somewhat higher temperatures, but transformable by heat, without substantial evaporation, into an infusible, more .or less gelat- 10118 mass, softening under the efiects of cat.

7. An insulatin composition for impregnating coils or H e purposes, containing a phenolic condensation product and a solvent therefor, said solventbein immiscible with water, possessing high die ectric pro erties, having a boiling-point above 120 and containing a liquid cyclic hydrocarbon and naphthalene, said condensation product and solvent proportioned to render the mass initially fluid or mobile at normal or somewhat higher temperatures, but transformable by heat, without' substantial evaporation, into an infusible, more or less gelat-. inous mass, softening under the effects of cat.

8. An insulatin composition for impregnating coils or 1' e purposes, containing a phenolic condensation product and a solvent therefor, said solvent'bein immiscible withmater, possessing high die ectric prope purposes, containing a p erties, having a boiling-point above 120 0., and containing a liquid cyclic hydrocarbon, naphthalene, and a comminuted inert filler, said condensation product and solvent proportioned to render the mass initially fluid or mobile at normal or somewhat higher temperatures, but 'transformable by heat, without substantial evaporation, into an infusible, more or-less gelatinous mass, softening under the effects of heat.

In testimony whereof I aflix my signature in presence of two witnesses;

LEO H. BAEKELAND. Witnesses:

R. I. HULSIZER, N. P. LEONARD. 

